JPH0550285A - Oxygen lean type reflow method and reflow device for circuit board - Google Patents

Abstract

PURPOSE:To provide the oxygen lean type reflow method and reflow device for circuit boards which can efficiently execute soldering with good quality. CONSTITUTION:The circuit board 12 to be subjected to reflow is subjected to preheating or solder melting in the state of rarefying the oxygen in a furnace by burning a combustion gas 5. A cooling catalyst or cooling water is passed in a tubular trap 10 and the moisture condensed to the outer side of the trap 10 is removed, by which the moisture in the furnace generated by the combustion of the combustion gas 5 is removed. The soldering with the good quality is efficiently executed in this way without oxidizing the circuit board the electrodes of parts and cream solder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board thin oxygen reflow method and a reflow apparatus for melting a cream solder after mounting an electric part on the circuit board coated with the cream solder.

[0002]

2. Description of the Related Art Conventionally, electrical parts are mounted on a circuit board,
In order to melt the electrode and the electrode of the component, the circuit board 12 is passed through the inside of the device provided with the electric heater 21 and the fan 11 as shown in FIG. 4, and the cream solder on the circuit board 12 is melted. It was done by doing.

[0003]

However, in the solder melting method as described above, the electrodes of the heated circuit board or the electrodes of the components are oxidized, or the solder is oxidized during preheating or melting to form solder holes, The circuit board needed cleaning. Further, as the lead pitch of IC parts becomes finer, solder balls sometimes short-circuit the electrodes and cause defects. Further, in the conventional reflow method, a weakly active flux was sometimes used to eliminate cleaning,
Since the activation power is weak, there is a problem that the electrodes of the circuit board and the electrodes of the components are not sufficiently wet with the solder.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a reflow method and a device therefor capable of efficiently performing high quality soldering.

[0005]

In order to achieve the above object, the reflow method of the present invention burns a gas such as methane gas (CH ₄ ), propane (CH ₈ ) and oxygen in a furnace, Filled with carbon dioxide or carbon monoxide,
The present invention is characterized in that the oxygen concentration ratio is relatively reduced, or hydrogen gas is flown to burn oxygen in the furnace to pass the circuit board through the oxygen-reduced furnace to melt the solder on the circuit board.

Further, the furnace is provided with a water trap for removing water generated when the gas is burned. In addition, a circuit board is placed in the furnace after the oxygen concentration in the furnace is lowered by installing or sequentially supplying a porous material such as metal or activated carbon, which easily oxidizes magnesium, manganese, aluminum, iron, etc. in the furnace. So that the solder on the circuit board is melted.

[0007]

According to the reflow method of the present invention, the electrodes of the heated circuit board and the electrodes of the parts are not oxidized, and the solder is not oxidized to become solder balls during preheating or melting.

Further, by providing a moisture trap for removing moisture generated when the gas is burned in the furnace, the humidity does not adversely affect the substrate and components.

[0009]

Embodiments of the reflow method of the present invention will be described below with reference to the drawings.

(Embodiment 1) In FIG. 1 showing the overall structure of a reflow apparatus, a circuit board 12 is conveyed from a right side of a main body 1 by a conveyor belt 2 and discharged at a left outlet. The reflow zone 17 is surrounded by a heat insulating material 3, and a gas supply unit 4 is installed above the heat insulating material 3, and a combustion gas 5 such as methane gas, propane gas, and natural gas and hydrogen are supplied from the outside to oxygen or outside air. The gas 6 is mixed in the mixer 7 at a rate of 0 to 90% and burned inside the main body 1. An ignition unit 8 and an oxygen sensor 9 are installed in the gas supply unit 4, and the oxygen concentration is fed back to the mixer 7 from the oxygen sensor 9. When the oxygen concentration is high, the concentration of oxygen or gas 6 such as the atmosphere supplied is reduced, and when the oxygen concentration decreases, the oxygen concentration is adjusted so that the combustion gas 5 is completely burned. A moisture trap 10 is installed below the gas supply unit 4. The water trap 10 arranges a tube cooled with a cooling catalyst or cooling water in the furnace to condense and adsorb the water generated together with carbon dioxide when the combustion gas burns, and discharge it to the outside.

A fan 11 is provided below this to circulate the air in the furnace to maintain a uniform temperature distribution. A heating heater 21 may be installed around the fan 11. In addition, a shield plate 13 is installed at the inlet and the outlet where the circuit board 12 is conveyed for the purpose of preventing the outflow of carbon dioxide generated by burning the gas and preventing the introduction of outside air. This shield plate 13 is a shutter type circuit board 1.
A method of opening and closing only when 2 passes is also used. It should be noted that an ultraviolet irradiation section may be provided in the zone 14 in the first partition of the furnace through which the circuit board 12 passes, and an adhesive curing section for curing the adhesive may be provided in the zone 15. In addition, the preheating zone 16 may be provided to preheat the circuit board 12, the cream solder placed on the circuit board 12, or parts.

(Embodiment 2) Next, Embodiment 2 of the present invention in which moisture generated from the combustion gas is absorbed by sequentially circulating the moisture absorber will be described with reference to FIG. The main body 1 is provided with the conveyor belt 2 as in the previous example, and the circuit board 12 is placed on the belt and conveyed from the inlet to the outlet. The moisture absorber 18 is filled with a substance that absorbs moisture, and this absorbs the moisture generated by burning the gas in the furnace. The moisture absorber 18 absorbs moisture in the furnace by being installed in the furnace or sequentially passing through the main body 1 by a transfer device (not shown).

(Embodiment 3) As a third embodiment, an example in which an oxygen absorber is installed in a furnace will be described with reference to FIG. Figure 3
In the inside of the main body 1, the heater 21 and the fan 1
1 is installed and hot air is circulated for reflow.
An oxygen absorber 22 is installed inside the main body 1, where the oxygen concentration in the furnace is reduced by absorbing oxygen to prevent oxidation of the solder, the circuit board and parts. The oxygen absorber 22 may be installed in the furnace or may be sequentially passed through the furnace by a transfer device (not shown) to absorb oxygen.
Further, the oxygen absorber 22 may be burned in the furnace to absorb oxygen. In that case, an ignition device is provided in the furnace. The oxygen absorber 22 is made of magnesium, manganese, aluminum, iron in the form of threads or powder. Other organic porous materials such as activated carbon may be used. In the above embodiment, the example in which the circuit board 12 is continuously conveyed by the conveyor belt 2 has been described, but the circuit board 12 may be carried into the furnace in batches. Further, after carrying in some of the circuit boards 12 into the furnace, the process may be performed by closing the inlet and outlet of the furnace.

[0014]

As is clear from the above description, the reflow method of the present invention reduces the oxygen concentration in the furnace, so that the electrodes of the heated circuit board and the electrodes of the parts are oxidized or preheated. The solder will not be oxidized and become solder balls when melted. This may eliminate the need for cleaning the circuit board. Further, as the lead pitch of the IC component becomes finer, the solder ball may short-circuit between the electrodes to cause a defect, but this does not occur, and the soldering at a fine pitch becomes easy. In addition, in the conventional reflow method, weakly active flux was sometimes used to eliminate cleaning, but due to its weak activation power, problems such as insufficient solder wetting on the circuit board electrodes and component electrodes occurred. Was.
However, according to the method of the present invention, since reflow is performed in a furnace with a low oxygen concentration, wettability does not decrease, and therefore, weakly active cleaning is unnecessary or a flux that can be easily cleaned can be used, and the running cost can be reduced. it can.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a configuration of a reflow device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a reflow device according to a second embodiment of the present invention.

FIG. 3 is a diagram illustrating a configuration of a reflow device according to a third embodiment of the present invention.

FIG. 4 is a diagram illustrating a configuration of a conventional reflow apparatus.

[Explanation of symbols]

 5 Combustion Gas (Gas) 10 Moisture Trap (Tubular Trap) 12 Circuit Board 18 Moisture Absorber 22 Oxygen Absorber

Claims (10)

[Claims] 1. A thin oxygen reflow method for a circuit board, comprising preheating or melting solder in a state where oxygen in the furnace is diluted by burning gas in the circuit board to be reflowed. 2. A thin oxygen reflow device for a circuit board, which is equipped with a combustor for burning gas to dilute oxygen in the furnace. 3. The water in the furnace generated by the combustion of gas is removed by flowing a cooling catalyst or cooling water into a tubular trap in the furnace to remove the water condensed on the outside of the trap. Oxygen diluted thin reflow method for circuit boards. 4. A means for removing water in the furnace generated by combustion of gas by flowing a cooling catalyst or cooling water into a tubular trap in the furnace and removing water condensed outside the trap is provided. An oxygen dilute thin reflow device for a circuit board according to claim 2. 5. The oxygen dilute reflow method for a circuit board according to claim 1, wherein the moisture absorbent is installed in or sequentially supplied to the furnace to remove moisture in the furnace generated by combustion of gas. 6. The oxygen dilute reflow device for a circuit board according to claim 2, further comprising means for installing or sequentially supplying a moisture absorbing material in the furnace to remove moisture in the furnace generated by combustion of gas. 7. A powder or thread-like cut product of a metal that easily oxidizes, such as magnesium, manganese, aluminum or iron,
Or, a porous material such as activated carbon is installed in the furnace or sequentially supplied, and the oxygen concentration in the furnace is lowered by burning them.
A method for diluting oxygen in a circuit board, in which the circuit board to be reflowed is preheated or solder is melted while oxygen in the furnace is diluted. 8. A powder or thread-shaped cut product of a metal that is easily oxidized, such as magnesium, manganese, aluminum, or iron,
Alternatively, a porous material such as activated carbon is installed or sequentially supplied to the outside air inlet inside or outside the furnace, and the reflowed circuit board is equipped with means for lowering the oxygen concentration in the furnace by burning them. Oxygen thin reflow device for circuit boards that preheats or melts solder in a dilute state. 9. A powder or thread-shaped cut product of a metal that is easily oxidized, such as magnesium, manganese, aluminum, or iron,
Alternatively, a container filled with a porous material such as activated carbon is placed in the furnace or sequentially supplied, and the oxygen concentration in the furnace is lowered by opening the container in the furnace.The circuit board to be reflowed is diluted with oxygen in the furnace. Oxygen thin thin reflow method of circuit board which preheats or melts solder under the condition. 10. A powder or thread-like cut product of a metal that easily oxidizes, such as magnesium, manganese, aluminum or iron,
Alternatively, a container filled with a porous material such as activated carbon is installed in the furnace or sequentially supplied, and the container is opened in the furnace to reduce the oxygen concentration in the furnace. Oxygen thin reflow device for circuit boards that preheats or melts solder while diluting oxygen in the above.